This application is based on Japanese Patent Applications No. 2001-46530 filed on Feb. 22, 2001, No. 2001-78062 filed on Mar. 19, 2001, No. 2001-78066 filed on Mar. 19, 2001, No. 2001-202710 filed on Jul. 3, 2001, No. 2001-366021 filed on Nov. 30, 2001 and No. 2001-383366 filed on Dec. 17, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an oil condition sensor which detects the condition of oil.
2. Description of the Related Art
Along with the use of oil for hydraulic control or lubrication served for vehicle or the like, a foreign material is mixed into oil or oil is degraded as time lapses. The PH value which indicates acidity or alkalinity of oil can indicate a condition of oil. The change of PH value expresses the deterioration of the condition of oil. Accordingly, the oil exchange period can be known by detecting the condition of oil. For example, an oil condition sensor which detects the condition of oil can be constituted of a reference electrode whose potential is held at a substantially fixed value irrespective of the PH value of oil and a comparison electrode whose potential is changed in response to the PH value of oil. When the PH value of oil is changed along with the deterioration of oil, the potential difference between both electrodes is changed.
JP-A-7-77514 discloses a conventional oil condition sensor. But the sensor has a drawback that the number of parts is increased so that the man-hours for assembling is increased. JP-A-6-281619, JP-A-7-140111, JP-A-5-5720 and U.S. Pat. No. 5,523,692 also disclose oil condition sensors. However, it has been difficult to obtain the compact configuration and the wide electrode area. Further, these publications fail to disclose practical structures.
In general, when the current leaks between electrodes, the accuracy of measuring potential between the electrodes is lowered and hence, the reliable insulation between the electrodes is required. Further, when the resistance between the electrodes of the oil condition sensor is large, the accuracy of measuring potential between the electrodes is lowered and hence, it is necessary to lower the resistance between the electrodes.
It is an object of the present invention to provide an oil condition sensor which can reduce the number of parts, can miniaturize the sensor and can detect the condition of oil and a method for making the oil condition sensor.
It is another object of the present invention to provide a miniaturized oil condition sensor which can detect an oil level in addition to the condition of oil.
According to the oil condition sensor of the present invention, respective electrodes are formed in a cylindrical shape. Therefore, the number of parts can be decreased and the man-hours for assembling can be reduced. Further, the detection accuracy of the condition of oil can be enhanced without increasing the size or diameter of the oil condition sensor.
Each electrode may be provided with communication holes which allow the inside and the outside thereof to communicate with each other. Since oil flows between the inside and the outside through the communication holes, it is possible to improve an oil circulation between the electrodes whereby the condition of oil can be detected with high accuracy.
The oil level sensor may be provided to the inside of the electrode. Due to such a constitution, man-hours for mounting the sensors on an oil pan or the like can be decreased. Further, insertion holes which are served for allowing the insertion of the sensors provided with a condition sensor and the oil level sensor into the oil pan from the outside can be made small.
With respect to mounting portions of both electrodes, at least one of the mounting portions may be bent to be away from the other mounting portion. Since the surface distance of a support member from one mounting portion to the other mounting portion, that is, the creepage distance can be elongated, a leak current can be reduced.